Valves of interest for use with the present invention include but are not necessarily limited to rotary valves such as plug valves and ball valves. Furthermore, valves of interest may use various types of seals including O-ring seals, metal-to-metal seals, grease seals, TEFLON.RTM. seals, and the like. The closure element, such as the rotatable plug in a plug valve, may be floating or non-floating. As well, the seat elements may be of the type that are rigid or floating or some combination thereof.
Gas seals, as opposed to liquid seals, tend to be the most problematic type of seal to reliably effect within a valve. With grease seals and TEFLON.RTM. seals, the leakage of lubricant and wear of the TEFLON.RTM. material may result in a gas seal that deteriorates in sealing ability as the valve is cycled between the open and closed position. Friction created between other types of seal elements and a floating plug closure element may be so problematic due to repeated closing and opening of the valve that a gas tight seal may sometimes exist for only a few cycles. Friction also exacerbates the problems of grease seals and TEFLON.RTM. seals.
In many valves, the seal of the valve is provided only by the seal formed by downstream valve seat elements. In valves that seal both upstream and downstream, when the valve is closed and the upstream seat elements leak, then leakage will typically occur through the bonnet and then through the downstream seat elements. Obviously, it has long been highly desirable to avoid such leakage.
Consequently, there has been a long felt need in the industry for a valve with seating elements that address the above problems to effect a reliable seal even when the fluid to be sealed is a gas, when the valve is cycled many times, and when the upstream seal leaks with the valve closed. Those skilled in the art will appreciate the present invention that addresses these and other problems.